A continuing area of developing technology involves the transfer of data between a main host computer system and one or more peripheral terminal units. To this end, there has been developed I/O subsystems which are used to relieve the monitoring and housekeeping problems of the main host computer and to assume the burden of controlling a peripheral terminal unit and to monitor control of data transfer operations which occur between the peripheral terminal unit and the main host computer system.
A particular embodiment of such an I/O subsystem has been developed which uses peripheral controllers known as data link processors whereby initiating commands from the main host computer are forwarded to a peripheral-controller which manages the data transfer operations with one or more peripheral units. In these systems the main host computer also provides a "data link word" which identifies each task that has been initiated for the peripheral-controller. After the completion of a task, the peripheral-controller will notify the main host system with a result/descriptor word as to the completion, incompletion or problem involved in the particular task.
These types of peripheral-controllers have been described in a number of patents issued to the assignee of the present disclosure and these patents are included herein by reference as follows:
U.S. Pat. No. 4,106,092 issued Aug. 8, 1978, entitled "Interface System Providing Interfaces to Central Processing Unit and Modular Processor-Controllers for an Input-Output Subsystem", inventor D. A. Millers, II.
U.S. Pat. No. 4,074,352 issued Feb. 14, 1978, entitled "Modular Block Unit for Input-Output Subsystem", inventors D. J. Cook and D. A. Millers, II.
U.S. Pat. No. 4,162,520 issued July 24, 1979, entitled "Intelligent Input-Output Interface Control Unit for Input-Output Subsystem", inventors D. J. Cook and D. A. Millers, II.
U.S. Pat. No. 4,189,769 issued Feb. 19, 1980, entitled "Input-Output Subsystem For Digital Data Processing System", inventors D. J. Cook and D. A. Millers, II.
U.S. Pat. No. 4,280,193 issued July 21, 1981, entitled "Data Link Processor for Magnetic Tape Data Transfer System", inventors K. W. Baun and J. G. Saunders.
U.S. Pat. No. 4,313,162 issued Jan. 26, 1982, entitled "I/O Subsystem Using Data Link Processors", inventors K. W. Baun and D. A. Millers, II.
U.S. Pat. No. 4,322,792 issued Mar. 30, 1982, entitled "Common Front-End Control for a Peripheral Controller Connected to a Computer", inventor K. W. Baun.
The above patents, which are included herein by reference, provide a background understanding of the use of the type of peripheral-controllers known as "data link processors", DLP, used in a data transfer network between a main host computer and peripheral terminal unit.
In the above mentioned Baun patent, there was described a peripheral-controller which was built of modular components consisting of a common front end control circuit which was of a universal nature for all types of peripheral controllers and which was connected with a peripheral dependent board circuit. The peripheral dependent circuit was particularized to handle the idiosyncrasies of specific peripheral terminal units.
The present disclosure likewise uses a peripheral-controller (data link processor) which follows the general pattern of the above described system, in that the peripheral-controller uses a common control circuit or common front end which works in coordination with a peripheral dependent circuit which is particularly suited to handle a specific type of peripheral terminal unit, such as a Tape Control Unit (TCU) which connects to one or more magnetic tape units.